This invention is related to the field of dual-band antennas. More particularly, this invention relates to a tapered slot antenna with broadband characteristics whose beamwidth is stable over both the PCS (1850-1990 MHz) and the cellular bands (824-894 MHz).
In the field of mobile communication, there are two major frequency bands, PCS and cellular. In an effort to reduce size, power consumption and cost, it would be optimal to use one antenna for both frequency bands. Current dual-band antennas use two separate columns of radiating elements (e.g., dipoles), one for PCS and the other for cellular. As a result, power is sent in unequal amounts to the left or the right of the boresight, i.e., it produces an asymmetrical beamwidth pattern. The amount of power differential varies with frequency.
For example, FIGS. 1 and 2 disclose the use of two separate columns of radiating elements (e.g., dipoles), one for PCS and the other for cellular. Note the asymmetry in the beamwidths produced by the cellular and the PCS beamwidths. (See FIGS. 3 and 4). The beamwidth produced over he PCS frequency range is skewed to the left of the boresight when compared to the beamwidth produced by the antenna over the cellular bandwidth. This illustrates how the antenna sends the power in unequal amounts to the left or right of the boresight depending upon the frequency. Another disadvantage over using separate columns of dipoles for the two bandwidths is that two connectors are needed, one for each column of dipoles.
FIG. 5 discloses the use of concentric columns of radiating elements (e.g., dipoles) one for PCS (center column) and the surrounding columns for cellular. Although it produces stable, centered beamwidths for both ranges of frequency (see FIGS. 6 and 7), its beamwidth is too narrow. That is, it is not capable of generating a 90 degree beamwidth pattern since both bands would only have a single column that would want to be centered in the antenna.
To produce a symmetrical pattern, one row of dipoles centered in the middle of the reflector is needed. However, this alone is not enough to produce a symmetrical beamwidth pattern. For example, FIGS. 8a, 8b and 8c illustrates a single column of radiating elements in which the radiating elements are circular dipoles in which the radius of curvature of the electrically conductive members defining the tapered slot of the dipole is fixed. This radiating element is disclosed in U.S. Pat. No. 6,043,785, hereby incorporated by reference. As disclosed in FIG. 9, while the antenna will match to 50 ohms across both bands, the beamwidth created using a single column of circular dipoles is not stable over the PCS and cellular bandwidths. That is, there is a large variation in beamwidth when the antenna is used in both the PCs and in the cellular bandwidths. For example, the cellular beamwidth pattern is broadened 20 degrees when compared to the PCS bandwidth.
In summary, current 90 degree antennas capable of covering both the PCS and the cellular bandwidths are either not stable or send power in unequal amounts to the left or the right of the boresight, i.e., it produces an asymmetrical beamwidth pattern.
The present invention is a broad band antenna for use in both the PCS and the cellular bandwidths. It comprises an array of tapered slots which are mounted on a reflector. Furthermore, a feedline is operably connected to said array of tapered slots for routing RF and microwave signals. Each of the tapered slots consists of a pair of elliptically shaped members, having a gap between said pair of elliptically shaped members. The slot is exited by a section of feedline that runs perpendicular to the gap. A plurality of tapered slots may be arrayed, with a space between each of said tapered slots. Said space serving to create a desired inter-element spacing.
In another preferred embodiment, each of said plurality of elliptically shaped members is a dipole wherein the height and width of the elliptically shaped members comprises a ratio of 2:1.
In still another preferred embodiment, the reflector further comprises at least one main reflector operably connected to the ends of said reflector which run parallel to array of tapered slots and at least one sub-reflector operably connected between the main reflectors and the array of tapered slots.
In still another preferred embodiment, the antenna is an element of a telecommunications system.